Discharge lamp having vapor pressure control means

ABSTRACT

A device for use with fluorescent lamps, including a mercury and metal amalgam disposed on a bimetallic element, said element being attached to a supporting member which is resiliently mounted against the lamp wall. The device is so placed inside the tube that the amalgam is moved towards a colder area of the tube as the tube heats, thereby providing substantially constant pressure and luminous flux output over a wide temperature range.

United States Patent Raymond Claude Emile Boucher La Garenne-Colombes;

Jean-Louis Marie Otto, Boulogne; Andre Marc Victorin Taxil, RueilMalmaison, all

Inventors of France Appl. No. 837,500 Filed June 30, 1969 Patented Jan.11, 1972 Assignee International Standard Electric Corporation New York,N .Y. Priority July 15, 1968 France 159,213

DISCHARGE LAMP HAVING VAPOR PRESSURE CONTROL MEANS 9 Claims, 8 DrawingFigs.

11.8. C1 313/174, 3 1 3/ 109 Int. Cl ..ll0lj 17/26, H01j 61/24 Field ofSearch 3 I 3/109,

Primary Examiner-John Kominski Assistant Examiner Palmer C. DemeoAt!0rneysC. Cornell Remsen, .Ir., Walter J. Baum, Paul W. Hemminger,Percy L. Lantzy, Philip M. Bolton, Isidore Togut, Charles L. Johnson,Jr.

ABSTRACT: A device for use with fluorescent lamps, including a mercuryand metal amalgam disposed on a bimetallic element, said element beingattached to a supporting member which is resiliently mounted against thelamp wall. The device is so placed inside the tube that the amalgam ismoved towards a colder area of the tube as the tube heats, therebyproviding substantially constant pressure and luminous flux output overa wide temperature range.

" PATENTEnJmnmz 5 I sum 2 or 3 Inventors RAYMOIvo C. acumenJEAN-10018;", ar

g q M. v. TAX/L Attorney PATENTED m1 1 1972 3634717 SHEET 3 [IF 3 IInventor; RAYMOND c. c. lOllCI/ER JEAIV'LQUIS M. OTTO mvon n. v. TAX/1.

A llorney DISCHARGE LAMP HAVING VAPOR PRESSURE CONTROL MEANS BACKGROUNDOF THE INVENTION in a classical fluorescent tube for a tube walltemperature of approximately 40 C.

When, due to the variation of the ambient temperature and/or to achangein the output power of the tube, the temperature of the wallvaries on either side of the optimum temperature, the mercury vaporpressure also varies, and therefore the efficiency of the resonantradiation decreases. The same is true of the luminous efficiency of thetube and thus also for the luminous flux supplied by the tube.

In order to enable operation of the tube at temperatures and/or otheroutput powers than those of maximum efficiency for a classicalfluorescent tube, it is known in the prior art to introduce into thetube an amalgam, based for example on indium or cadmium combined withmercury. Depending on the composition of this amalgam, and depending onthe temperature of which it is brought due to its position in the tube,the optimum operating temperature of the tube is shifted.

SUMMARY OF THE INVENTION An object of the present invention is thereforeto provide a device for use with a low pressure mercury vapor dischargetube so that the luminous flux of the tube remains substantiallyconstant over a wide temperature range.

It is a further object of the present invention to provide a device foruse with a low-pressure mercury vapor discharge tube so that the optimumoperational pressure is reached rapidly after the ignition of the tube.

According to the present invention there is provided, inside alow-pressure mercury vapor discharge tube, an amalgam disposed on anelement, the shape of the element varying with temperature, so that theamalgam moves towards the-colder regions of the lamp when thetemperature increases.

It is a feature of this invention to connect said element to a supportmember which is in contact with the tube wall so as to maintain theposition of the amalgam and element within the tube.

Further objects and features of this invention will become more apparentby reference to the following description taken in conjunction with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents curves indicatingthe variation of the luminous flux output of a fluorescent tube withtemperature;

FIGS. 2, 3 and 4 represent preferred embodiments of the device accordingto the present invention;

FIG. 5 is a view of the position of the device of FIG. 3 inside adischarge tube; and

FIGS. 6, 7 and 8 represent additional preferred embodiments of theinventive device located inside discharge tubes.

DESCRIPTION OF THE PREFERRED EMBODIMENT The curve of FIG. 1 representsthe relative variation of the luminous flux F of a low-pressure mercuryvapor discharge tube with the temperature T of the tube, that is, withthe temperature of the wall of the tube. This curve shows that the tubeprovides 90 percent of the maximum flux for wall temperatures rangingbetween 29 and 48 C.

As has been previously mentioned, when it is required to operate thetube at higher temperatures, an amalgam which can be based on indium orcadmium is introduced into the tube. In the usual method of manufactureof a fluorescent tube, the mercury and the metal which constitutes thebase of the amalgam are generally introduced separately, the amalgambeing formed afterwards. By using amalgams of differing compositionsand/or by varying the temperatures of the amal- .gam by changing theposition of the amalgam in the tube, lu-

minous flux curves which are similar to curve 1 of FIG. I are obtained,but the curves are shifted along the temperature axis as shown by thedashed line curve 2 and FIG. 1. In this manner tubes having difi'erentoptimum temperatures are obtained.

It will be observed that in a tube with amalgam, the pressure is imposedby the temperature of the amalgam, whereas in a tube with only mercury,the pressure is imposed by the temperature of the coldest point of thetube, that is, the temperature of the tube wall. Therefore, the amalgammust be at a temperature such that the pressure it imposes due to itstemperature should be lower than the pressure provided by mercury alone.If this were not the case, the mercury would distill toward the wall andthe tube would behave in the same way as a tube using mercury alone.

As previously stated, this invention proposes the changing of theposition of the amalgam inside the tube, the relation to the temperatureof said tube, the change of position being such that the amalgam movestowards colder regions, that is, toward the walls of the tube while thetube is being heated.

FIG. 2 shows one preferred embodiment of a device which fulfills theobject of the present invention. The device is composed of a bimetallicstrip 4 one end of which is fixed to a support or clip 6, while anamalgam 5 is fixed to the other end of the strip 4. The clip 6 maycomprise a metallic strip bent in several places, the elasticity ofwhich enables both the folding over of itself so as to facilitate theintroduction of the clip into the tube and also allows the clip to restagainst the walls of the tube so as to maintain the clip and bimetallicstrip 4 in place within the tube regardless of the tube position.Further, the clip 6 assures a thermal contact with the wall. If therigidity of the device obtained by means of the single clip 6 is notsufficient, provision can be made for the use of a second clip as shownin FIG. 3.

FIG. 4 represents another embodiment of the clip 6 which is in the shapeof a closed polygon.

FIG. 5 represents the position in the tube 7 of the subject invention,in particular, the embodiment shown in FIG. 3. Although the device, inparticular the amalgam, is shown located at the midpoint of thelongitudinal axis of the tube, that is, between the discharge electrodesat the ends of the tube, it is to be understood it may be locatedanywhere within the tube where the results are optimum.

It is possible to use the same amalgam in either a classical tube or ina tube known as a high-output power" tube of the same length, by varyingthe length of the bimetallic strip. The bimetallic strip will be longerin the case of a high-output power tube than in a classical tube, sincethe difference in temperatures between the discharge axis and the wallis more important in a high-output power" tube than in a classical tube.

FIG. 6 represents a cross section of a discharge tube 7 in which islocated a device embodying the features of the present invention. Thisdevice consists of a bimetallic element 4, or any dilatable element, onwhich is disposed the amalgam 5. The ends of the element 4 are arrangedin two notches 8 and 10 of a support member 9, the support restingagainst the wall of the tube 7. The support 11 may comprise an elasticmetallic strip bent in the shape of a square, the apexes of whichconstitute notches such as those referenced 8 and 10.

It will be understood by those skilled in the art that the length of thedilatation element 4 must be such that it remains in the notches at thelowest temperature that the tube experiences during the time that thetube is off. It will also be understood that the notches 8 and 10 andthe ends of the dilatable element must be joined in such a way thatneither end can escape from its notch when the temperature of the tubeincreases, thereby increasing the camber of the dilatable element 4,especially when the camber becomes equal to the radius of the tube. Forthis purpose the notches and dilatable element may be arranged as shownin FIG. 7, where discs or cylinders 13 and 14 are connected to the endsof the dilatable element 4. The discs or cylinders are fitted intonotches l1 and 12 which have a circular cross section in such a way asto prevent the escape of either end of the dilatable element 4 when thecamber of said element increases. The notches 8 and 10 of FIG. 6 and 11and 12 of FIG. 7 are also shaped, obviously, to prevent the escape ofthe dilatable element when the tube is in a vertical position. Althoughthe notches shown in FIGS. 6 and 7 are diametrically opposed, therelative positions of the two notches may be in any relation desired.Further, although the amalgam is preferably disposed in the middle ofthe dilatable elements so that it may have maximum displacement, it mayalso be disposed at any other point on the dilatable element if aparticular adjustment is desired.

Although FIGS. 2, 3, 4, 6 and 7 have shown an element, the shape ofwhich varies with temperature, configured as a bimetallic strip,elements in other configurations which are distorted by temperaturevariations may be used. Thus, FIG. 8 illustrates a tube 7 in which aspiral 17 comprising a bimetallic strip is utilized, the spiral 17 beingconnected to a support 9 which rests against the wall of the tube. End16 of the spiral 17 is free and has disposed thereon the amalgam 5. Theother end of the spiral 17, end 15, is fixed to said support 9. As inthe previously discussed embodiments, the displacement of the end 16must be such that the amalgam approaches the wall of the tube as thetemperature increases.

Utilization of the inventive device in conjunction with a fluorescenttube will result in a temperature versus luminous fiux curve such asthat shown by the dashed line curve 3 of FIG. 1. From this curve it isseen that at least 90 percent ofthe maximum flux output is provided overa much greater temperature range than heretofore realizable. The devicesembodying the subject invention which are illustrated in FIGS. 2, 3, 4,5, 6, 7 and 8, further improve the performance of a fluorescent tube inthat they provide quick mercurization during he ignition of the tube.This is due to the fact that when the tube is ignited the amalgam isclose to the discharge axis and therefore heats more quickly than itwould in a tube comprising an amalgam fixed to the tube. This causes themercury to vaporize more quickly than it would if the amalgam were fixedto the tube and therefore the optimum mercury vapor pressure is reachedmore quickly.

To instruct those who wish to use the device embodying the subjectinvention with classical fluorescent tubes it is noted that the deviceis usually introduced into the tube after the powdering and rebumingprocess, well known in the fluorescent tube art, is completed. Themercury is introduced in the conventional way in the form of a liquiddrop, the weight of which depends on the length of the tube and therange of temperatures under which it is desired that the tube operate.

We claim:

1. In a low-pressure mercury vapor discharge lamp including an elongatedenvelope having a longitudinal axis, a pair of electrodes sealed atopposite ends of said envelope, and a mercury and metal amalgam withinsaid envelope, the improvement comprising control means, located withinsaid envelope and intermediate said electrodes, for moving said amalgamaway from said longitudinal axis when said lamp is ignited and toward acolder area of said envelope in response to temperature variations assaid lamp is heated, said means including a bimetallic element, saidamalgam being disposed on and directly fixed to said element.

2. In a discharge lamp according to claim 1, further comprising asupporting member, at least one end of said bimetallic element beingconnected to said member, and said member being resiliently mountedagainst and in contact with the envelope of said lamp.

3. In a discharge lamp according to claim 3, wherein said element is inthe shape of a strip.

4. In a discharge lamp according to claim 3, wherein said element is inthe shape of a spiral.

5. In a discharge lamp according to claim 4, wherein said member isformed with notches therein and the ends of said strip are disposedwithin said notches.

6. In a discharge lamp according to claim 3, wherein said supportingmember comprises a metallic strip bent in several places.

7. In a discharge lamp according to claim 3, wherein said supportingmember comprises a metallic strip in the shape of a closed polygon.

8. In a discharge lamp according to claim 6, wherein said supportingmember is in the shape of a square, said notches being formed at atleast two of the corners of said square.

9. In a discharge lamp according to claim 5, wherein said supportingmember is in the shape of a square and wherein one end of said spiralelement is connected to one side of said square.

1. In a low-pressure mercury vapor discharge lamp including an elongated envelope having a longitudinal axis, a pair of electrodes sealed at opposite ends of said envelope, and a mercury and metal amalgam within said envelope, the improvement comprising control means, located within said envelope and intermediate said electrodes, for moving said amalgam away from said longitudinal axis when said lamp is ignited and toward a colder area of said envelope in response to temperature variations as said lamp is heated, said means including a bimetallic element, said amalgam being disposed on and directly fixed to said element.
 2. In a discharge lamp according to claim 1, further comprising a supporting member, at least one end of said bimetallic element being connected to said member, and said member being resiliently mounted against and in contact with the envelope of said lamp.
 3. In a discharge lamp according to claim 3, wherein said element is in the shape of a strip.
 4. In a discharge lamp according to claim 3, wherein said element is in the shape of a spiral.
 5. In a discharge lamp according to claim 4, wherein said member is formed with notches therein and the ends of said strip are disposed within said notches.
 6. In a discharge lamp according to claim 3, wherein said supporting member comprises a metallic strip bent in several places.
 7. In a discharge lamp according to claim 3, wherein said supporting member comprises a metallic strip in the shape of a closed polygon.
 8. In a discharge lamp according to claim 6, wherein said supporting member is in the shape of a square, said notches being formed at at least two of the corners of said square.
 9. In a discharge lamp according to claim 5, wherein said supporting member is in the shape of a square and wherein one end of said spiral element is connected to one side of said square. 